(Revised Abstract) Description: The cerebral cortex is vitally important for perception and thought. Understanding how the cortex works is one of the great unsolved scientific problems. We have been studying the primary visual cortex, V1, in order to understand its role in vision and also because the V1 is one of the best-understood regions of the cerebral cortex. On the one hand we often have detailed knowledge of neuronal firing in V1 to an array of visual stimuli, obtained from extracellular recording. On the other hand, from anatomical studies, we know about the intricate neuronal architecture and the patterns of synaptic connections both within V1 and between V1 and extra-striate cortex. In order to understand such a complicated neuronal network, modeling how cortical neurons interact within the network is crucial. At present, there is one link that is missing that if present would enable much more realistic modeling of the cortex: the link between structure and function. In this application we are proposing experiments to pilot an extension of juxtacellular recording using a "loose" patch method (JC-LP, juxtacellular-loose patch). Development of this technique would allow us to characterize and stain neurons in visual cortex in vivo and would thereby provide the link between function and structure.